Devices of this type are known, provided with drive shafts having the possibility of changing the relative position of control cams relative to said shafts.
Signal actuators of this type are already known in the prior art, for example from U.S. Pat. No. 5,305,781. In this known device, in order to locally adjust the signal actuator it is necessary to provide for a possibility of positioning the control cams into multiple angular positions relative to the drive shaft; it is therefore known, for example, to provide a fastening by shape-coupling of the control cams through a toothing of the components mentioned hereinabove. In this case, to make any adjustments it is necessary to axially move at least one control cam provided with an inner toothing beyond the outer toothing engagement zone of the drive shaft, in order to carry out the desired adjustment of an intermediate zone of the drive shaft not provided with toothing. Afterwards it is necessary to rearrange the control cam to the original axial position for carrying out a new shape coupling again. It is apparent that such an adjustment is excessively expensive and not practical, in particular in the case a plurality of control cams is arranged axially superimposed on one another and it is disadvantageously necessary to move at least the control cam to the bottom end of the drive shaft. In such a situation, it may understandably occur that the top control cam originally located in the correct angular position relative to the drive shaft, after the adjustment operation that has caused its separation and the subsequent reintroduction, is in an incorrect angular position relative to the drive shaft and that this requires a further adjustment. Moreover, as disclosed for example in U.S. Pat. No. 5,223,822, it is known to provide the control cams with a front toothing that interacts respectively with a front toothing on a seat of the drive shaft. With the aid of a spring acting in axial direction, the two correspondingly coupled front toothing sets are pressed against one another so as to form a torsion-resistant connection between the control cam and the drive shaft. In this way, in case of adjustment, by acting against the spring force it is possible to temporarily disconnect the control cam from the fixed toothing on the shaft and after the transfer to the desired angular position, replace the cam coupled to the fixed toothing of the drive shaft, without the action of a further external force. This allows firmly coupling the control cam to the drive shaft, allowing operating conditions with high angular accelerations while ensuring that the angular position of the control cam relative to the drive shaft is maintained. It is understood, however, that the adjustment principle mentioned above is not advantageous as it requires a greater construction complexity and implies an increase of the overall dimensions of the device, as spaces overlying and underlying the control cams are to be provided for the disengagement and the optional rotation of the control cams, with clear disadvantages.
It is also known in the art, for example in EP-A-0921338, a coupling system between at least two stacked control cams and an hollow drive shaft provided with a limited toothed portion of the outer surface of the hollow drive shaft for the remainder free from toothing that has an elastic flexibility degree in radial direction. Such drive shaft is connectable through the above partial outer toothing to the stacked control cams; in this case, the adjustment is entrusted to the elastic flexibility of the toothed portion of the outer surface of the drive shaft. In this way, in case of adjustment, by acting with an appropriate tool against the elastic force of said toothed portion, it is possible to arrange the control cams in the desired angular position. Actually, the described solution exhibits small overall dimensions, but the engaging limited to the toothed portion of the outer surface of the hollow shaft, by offering a resistance due to said partial toothing only, defines an upper limit to the inertial action applicable to the control cam and drive shaft coupled system. Beyond said limit, the relative position between the drive shaft and the control cams is inevitably lost.
There is therefore the need of providing a signal actuation device for an adjustment control which should be useful also in operating conditions with high angular accelerations, ensuring a firm fixing between control cams and drive shaft; moreover, said device must have small overall dimensions.